Conventionally, in a known clothes dryer, a drying air heated by a burner is introduced by a fan into a drum into which clothes to be dried are introduced, and the drying air is discharged from a back side of the main body.
FIG. 4 is a flowchart showing processing procedures of a drying operation of a conventional clothes dryer. The clothes dryer process shown in FIG. 4 is generally performed by a control unit, and when a start button is pressed, the operation is started to proceed to step T1.
<Step T1>
In step T1, the control unit starts rotations of the drum and the fan. As a result, the supply of drying air to the drum and the exhaust of drying air from the drum are started.
<Step T2>
In step T2, the control unit ignites the burner. As a result, the supply of high-temperature drying air to the drum is started.
<Step T3>
In step T3, the control unit starts counting the operation time.
<Step T4>
In step T4, the control unit determines whether or not the operation time has reached the end time and determines whether or not to end the operation. If it is determined that the operation is to be ended, the process proceeds to step T10, and if it is determined not to end the operation, the process proceeds to step T5.
<Step T5>
In step T5, the control unit determines whether or not the exhaust temperature has reached an upper limit temperature. If it is determined that the exhaust temperature has reached the upper limit temperature, the process proceeds to step T6. If it is determined that the exhaust temperature has not reached the upper limit temperature, the process returns to step T4.
<Step T6>
In step T6, the control unit stops the burner. As a result, the drying air that is not heated and of substantially normal temperature is supplied to the drum, and hence the interior temperature of the drum is lowered.
<Step T7>
In step T7, the control unit determines whether or not the operation time has reached the end time, and determines whether or not to end the operation. If it is determined that the operation is to be ended, the process proceeds to step T10. If it is determined not to end the operation, the process proceeds to step T8.
<Step T8>
In step T8, the control unit determines whether or not the exhaust temperature has reached a re-ignition temperature. If it is determined that the exhaust temperature has reached the re-ignition temperature, the process proceeds to step T9. If it is determined that the exhaust temperature has not reached the re-ignition temperature, the process returns to step T7.
<Step T9>
In step T9, the control unit re-ignites the burner, and the process proceeds to step T4. As a result, the supply of the high-temperature drying air to the drum is resumed, and the interior temperature of the drum rises again.
<Step T10>
In step T10, the control unit stops the burner, and stops both of the rotation of the fan and the rotation of the drum. As a result, this flow is ended.
As described above, the existing clothes dryer suppresses the abnormal rise of the interior temperature of the drum and prevents the damage to the clothes due to the overheating by repeating the following processes. When the exhaust temperature from the drum reaches the predetermined upper limit temperature, the burner (heat source) is stopped so as to lower the interior temperature of the drum, and thereafter, when the exhaust temperature reaches the predetermined re-ignition temperature, the burner is re-ignited.
However, in the above-described drying operation, even after the exhaust temperature reaches the upper limit temperature, that is, after the moisture contained in the clothes decreases and at least some of the clothes have been almost dried and are excessively dried, the burner is re-ignited at once when the exhaust temperature is lowered to the re-ignition temperature. As a result, the interior temperature of the drum is kept high and the surface temperature of the clothes is kept rising. Such a state leads to a damage of clothes, and the above-described clothes dryer performing the existing drying operation has room for improvement in reducing clothing damages due to overheating.
To solve this problem, the following control may be considered: in the second half of the operation of repeatedly extinguishing/igniting the burner, the upper limit temperature is lowered, and the burner is stopped before the interior temperature of the drum rises excessively. However, the clothes dryer, especially the clothes dryer which the self-service laundry likes to use due to its characteristics, cannot distinguish the type, the weight, etc. of the clothes accommodated in the drum, it is difficult to determine when it is the second half of the operation, so it is difficult to adopt this control.